Continuity mistake: When Lois and Arthur are sitting at the end of the dock, (before Arthur begins to hear the piercing ringing sound) the position of the bikini lace hanging down Lois' back keeps changing between shots.
Continuity mistake: The water level in the glass that Lex taunts Aquaman with changes levels throughout the scene.
Answer: The kryptonite only creates mutations when it reacts with the environment and an individual. Remember, the FDA and several environmental groups did check out Smallville after the meteor shower, but found no danger in the rocks. Obviously they're not always emitting mutating rays, or all the flora and fauna of the surrounding area would be horribly mutated.
Phoenix